Molecular evidence for the gnathobasic derivation of arthropod mandibles and for the appendicular origin of the labrum and other structures

 Mandibles are feeding appendages functioning as ”jaws” in the arthropod groups in which they occur. Which part of this appendage is involved in food manipulation (limb tip versus limb base), has been used to suggest phylogenetic relationships among some of the major taxa of arthropods (myriapods, crustaceans, and insects). As a way to independently verify the conclusions drawn from previous morphological analyses, we have studied the expression pattern of the gene Distal-less (Dll), which specifies the distal part of appendages. Our results show, in contrast to the traditional view, that both insect and crustacean adult mandibles are gnathobasic, handling food with the basal portion of the appendage. Furthermore, as is evident by the reduction in the number of Dll-expressing cells in the later developmental stages, adult diplopod jaws are also gnathobasic. Thus, jaws of all mandibulates (myriapods, crustaceans, and insects) seem to have a similar gnathobasic structure. We have also found that Dll is expressed in the labra of all arthropod taxa examined, suggesting that this structure is of appendicular derivation. Additionally, the spinnerets and book lungs of spiders, long considered on other grounds to be modified appendages, express Dll, confirming this interpretation. This study shows that, in addition to their use in phylogenetic and population genetic studies, molecular markers can be very useful for inferring the origins of a particular morphological feature. Received: 12 January 1998 / Accepted: 23 March 1998     

Human placental estradiol 17 beta-dehydrogenase. Identification of a single histidine residue affinity-labeled by both 3-bromoacetoxyestrone and 12 beta-bromoacetoxy-4-estrene-3,17-dione

Human placental estradiol 17 beta-dehydrogenase (EC 1.1.1.62) was affinity-labeled at pH 6.3 by 3-bromo[2'-14C]acetoxyestrone and 12 beta-bromo-[2'-14C] acetoxy-4-estrene-3,17-dione (both are substrates) in separate incubations. The affinity-alkylated enzyme samples were then treated separately as described below. Amino acid compositions of both samples revealed radioactive 3-carboxymethylhistidine. Tryptic digests of each sample were prepared, applied to Sephadex G-50, and 3-carboxymethylhistidine-bearing fractions identified. These peptides were further purified by cation exchange chromatography, gel filtration, and paper electrophoresis. The purified, 3-carboxymethylhistidine-bearing peptides labeled by the two steroids had identical electrophoretic mobilities at pH 6.5, 3.5, and 1.9. The amino acid sequence of the radioactive peptide alkylated by 3-bromo[2'-14C]acetoxyesterone was determined as: Leu-Ala-3-[14C]CmHis-Ser-Lys. The smaller quantity of peptide obtained from the inactivation with 12 beta-bromo[2'-14C]acetoxy-4-estrene-3,17-dione precluded the determination of its complete sequence. However, the first 3 residues were found to be Leu-Ala-3-[14C]CmHis and the amino acid composition showed that serine and lysine were also present. It is concluded that the steroid-binding site of human placental estradiol 17 beta-dehydrogenase contains a histidine residue which proximates the upper A-ring region of the steroid as it undergoes the reversible binding step.     

A model for the reaction pathways of the K+-dependent phosphatase activity of the (Na+ + K+)-dependent ATPase

$\text{(Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-dependent}$ ATPase preparations from rat brain, dog kidney, and human red blood cells also catalyze a K⁺-dependent phosphatase reaction. K⁺ activation and Na⁺ inhibition of this reaction are described quantitatively by a model featuring isomerization between E₁ and E₂ enzyme conformations with activity proportional to E₂K concentration:

Differences between the three preparations in $\text{K}{}_{0.5}$ for K⁺ activation can then be accounted for by differences in equilibria between E₁K and E₂K with dissociation constants identical. Similarly, reductions in $\text{K}{}_{0.5}$ produced by dimethyl sulfoxide are attributable to shifts in equilibria toward E₂ conformations. Na⁺ stimulation of K⁺-dependent phosphatase activity of brain and red blood cell preparations, demonstrable with KCl under 1 mM, can be accounted for by including a supplementary pathway proportional to E₁Na but dependent also on K⁺ activation through high-affinity sites. With inside-out red blood cell vesicles, K⁺ activation in the absence of Na⁺ is mediated through sites oriented toward the cytoplasm, while in the presence of Na⁺ high-affinity K⁺-sites are oriented extracellularly, as are those of the $\text{(Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-dependent}$ ATPase reaction. Dimethyl sulfoxide accentuated Na⁺-stimulated K⁺-dependent phosphatase activity in all three preparations, attributable to shifts from the E₁P to E₂P conformation, with the latter bearing the high-affinity, extracellularly oriented K⁺-sites of the Na⁺-stimulated pathway.     

Regional differences in the effects of insulin-induced hypoglycemia on phospholipid metabolism of rat brain

Insulin-induced hypoglycemia in rats may lead to stimulated brain activity and if severe enough, they may develop a stupor-coma condition. In this study, the effects of insulin-induced hypoglycemia on brain phospholipid metabolism were examined in rats which were prior injected with ³²Pi. Three hours after insulin injection (1 or 5 units/100 g body wt, i.p.), there was an increase (25%) in radioactivity of the lipid phase of cerebral cortex, but radioactivity in the cerebellum tended to decrease instead. Radioactivity in the aqueous phase of cortex was not altered after insulin injection, but that in the cerebellum was decreased by 30%. Differences were observed in labeling of individual phospholipids in response to the hypoglycemic treatment. A marked decrease in labelled phosphatidate was observed in the cerebellum from the hypoglycemic samples, but not in the cerebral cortex. In the cortex, hypoglycemic condition resulted in an increase in ³²Pi uptake into the phospholipids. However, the differences in the amount of label among individual phospholipids suggest that phosphatidylinositol and phosphatidylcholine are turning over more rapidly than other phospholipids. The hypoglycemic rats also showed a 3-fold increase in the brain free fatty acid level, but the level of diacylglycerol was not changed. Results thus suggested a correlation between the free fatty acid release and the increased turnover of phosphatidylinositol and phosphatidylcholine during brain stimulation due to insulin-induced hypoglycemia.     

The luminescent bacteria toxicity test: Its potential as an in vitro alternative

During the past several years, the use of animals for toxicity testing has come under critical surveillance. For ethical and economic reasons, various techniques have been developed and proposed as potential alternatives for some of the whole animal toxicity assays. One assay proposed as an alternative to animal testing is the luminescent bacteria toxicity test (LBT), provided under the trade name of Microtox®. The sensitivity and specificity of the LBT was compared with two commonly used toxicity tests–-the L-929 Minimal Eùgle's Medium (MEM) elution cytotoxicity test and the Draize test. Cytotoxicity and LBT test data from 709 medical device and biomaterial extracts were compared using a positive/negative ranking system which provided a measurement of false positive and false negative results. These data were compiled from nine separate laboratories producing or using a wide variety of biomaterials and medical device products. The LBT was more sensitive than the tissue culture assay and displayed few false negatives. LBT EC₅₀ values were compared with eye irritancy categories for a group of 34 chemicals and 27 personal care products. As with tissue culture, the LBT was more sensitive and produced minimal false negatives. The data from this study indicate the LBT has potential as a rapid, simple method to screen biomaterials and personal care products for toxicity and irritancy.     

Cryopreservation of isolated rat hepatocytes

Summary Isolated parenchymal hepatocytes from adult rats were frozen in media containing 10% glycerol, 10% dimethylsulfoxide (DMSO), or 20% DMSO. Three microsome-associated functions were compared in nonfrozen cells and cells frozen in each of the above cryoprotectant solutions. Freezing in DMSO maintains cytochromes P-450 and b₅ and NADPH-cytochrome C reductase at levels nearer to control values than does freezing in glycerol. Cells frozen and subsequently thawed and cultured for 24 h lose a greater amount of cytochrome P-450 than do nonfrozen cultured cells. The levels of cytochrome b₅ and reductase in frozen-thawed cells remain close to control values. Cell viability (trypan blue dye exclusion and percentage of attached cells) after freezing is maintained better using DMSO as a cryoprotectant. Dimethylsulfoxide protects the hepatocytes from freeze-induced damage to the extent that many viable cells attach to collagen-coated petri dishes, survive for at least 24 h, and still maintain significant levels of enzymes of importance to drug and carcinogen metabolism. This work was supported by Grant CA-30241 from the National Institutes of Health, Bethesda, Maryland.     

Preliminary crystaliographic data for glyceraldehyde-3-phosphate dehydrogenase from the thermophile Bacillus coagulons

Crystals of thermolabile glyceraldehyde-3-phosphate dehydrogenase from Bacillus coagulans suitable for high resolution X-ray crystallographic analysis have been grown from sodium citrate solutions by equilibrium dialysis. The space group is C222₁, with cell dimensions $\text{a = 95·6 (2)}\text{A}\text{?}\text{, b = 137·2 (3)}\text{A}\text{?}\text{and}\text{c = 131·9 (4)}\text{A}\text{?}$. The molecules have one crystallographically exact 2-fold rotation axis of symmetry.     

Activation of arachidonoyl-phosphatidylinositol and phosphatidylcholine turnover by K+-evoked stimulation of brain synaptosomes

The turnover of arachidonoyl groups in synaptosomal phospholipids after stimulation by K⁺ was examined. Raising the K⁺ concentration in the incubation medium from 5 to 55 mM caused a rapid hydrolysis of labeled arachidonate from the synaptosomal phospholipids. Under this condition, radioactivity released from phosphatidylinositols was proportionally higher than that from phosphatidylcholines. Hydrolysis of arachidonoyl group from phospholipids was correlated to an increase in radioactivity in the free fatty acid-ion complex which appeared in the interphase after extraction with chloroform-methanol 2:1 (v/v). The K⁺-evoked phospholipid hydrolysis and the formation of fatty acid-ion complex, were Ca²⁺-dependent. Phospholipid deacylation activity was localized mainly in synaptic vesicles and synaptic plasma membranes but not in the mitochondria. The stimulated turnover of synaptosomal phospholipids appeared to be mediated by the deacylation-reacylation mechanism, because similar treatment with high K⁺ stimulated the incorporation of labeled arachidonate into phosphatidylinositols and phosphatidylcholines of synaptosomes. The possible physiological implication of membrane lipid involvement in synaptic processes is discussed.     

Isolation of histidyl peptides of the steroid-binding site of human placental estradiol 17β-dehydrogenase

Human placental estradiol 17β-dehydrogenase (E.C. 1.1.1.62) was inactivated at pH 6.3 by 3-bromo[2′-¹⁴C]acetoxy-1,3,5(10)estratrien-17-one, a known substrate. The affinity-alkylated enzyme was then hydrolyzed by trypsin. Radioactive peptides were initially isolated by gel filtration and identified according to which residue was alkylated. Tryptic peptides containing radioactive 3-carboxymethylhistidyl residues were further purified by cation-exchange chromatography. The population of these peptides varied, depending upon the conditions of enzyme inactivation. With 60 μM 3-bromo[2′-¹⁴C]acetoxy-1,3,5(10)estratrien-17-one four major peptides (a,b,c,d) each containing radioactive 3-carboxymethylhistidine, were eluted from the cation-exchange column. The alkylation of all of these peptides was completely suppressed when the enzyme was inactivated in the presence of excess estradiol-17β. The presence of equimolar NADPH during incubation greatly enhanced the alkylation of all four peptides. In the presence of NADPH, estradiol-17β most significantly decreased the formation of peptide d. Peptide d was the only peptide identified when the concentration of the alkylating steroid was lowered to 6 βM, a value approaching the Km. These observations indicate that peptide d is a histidyl-bearing peptide from the steroid-binding site which proximates the steroid A-ring. They further suggest that with the affinity labeling steroid at higher concentrations other nonspecific, hydrophobic sites on the enzyme are occupied and labeled.     

Azido analogs of acridine: Photoaffinity probes for frameshift mutagenesis in Salmonella typhimurium

In order to identify a photoaffinity probe for 9-aminoacridine frameshift mutagenesis, 20 azido analogs of acridine were synthesized and tested in Ames' Salmonella tester strains, TA1535, TA1537, TA1538 and their corresponding excision-repair-proficient strains TA1975, TA1977, and TA1978, to determine their mutagenicity and toxicity relative to 9-aminoacridine. The substituent-mutagenicity patterns observed for these compounds agree very well with those obtained previously for non-azidoacridines. The results presented here show that the 2-azido-analog of 9-aminoacridine demonstrates biological activity similar to 9-aminoacridine prior to photolytic activation. With light activation, however, the 9-amino-2-azido derivative becomes more effective at producing frameshift mutations characteristics of 9-aminoacridine. Furthemore, this photolytic enhancement of mutagenesis appears to be due to the repairable lesion suggesting that covalent attachment of the drug occurs.